In an n channel MISFET and a p channel MISFET forming a CMIS (Complementary Metal Insulator Semiconductor) circuit, a silicon oxide film is used as a gate insulating film. Also, a polysilicon film or a multilayered film (polycide film) formed by stacking a metal silicide film such as a tungsten silicide film or a cobalt silicide film on a polysilicon film is used as a gate electrode formed on the gate insulating film.
However, in accordance with the trend of the scaling down of the MISFET size in recent years, the thickness of the gate insulating film has been rapidly reduced. As the film thickness of the gate insulating film is reduced, a phenomenon occurs, in which electrons pass through the gate insulating film due to the tunnel effect, which causes a problem of an increase in leakage current of the MISFET.
For its solution, the use of a high dielectric film with a dielectric constant higher than that of a silicon oxide film as a gate insulating film has been examined. When such a high dielectric film is used as a gate insulating film, an actual physical film thickness can be increased by a factor of “dielectric constant of the high dielectric film/dielectric constant of the silicon oxide film”, even if the capacitance in terms of the silicon oxide film thickness is the same. Accordingly, it is possible to reduce the leakage current (for example, see Japanese Patent Application Laid-Open Publication No. 2002-314074).